Every field updates together.
Switch between binary, octal, decimal and hexadecimal as you type, turn numbers into Roman numerals and back, or write them out in words. Very large numbers work too. It is free and runs in your browser.
How to convert a number
- Choose a tab: Number bases, Roman numerals or In words.
- For bases, type in any row and the others follow. Prefixes such as 0x and 0b work too.
- For Roman numerals, type a number to get the numeral, or a numeral to get the number.
- For words, type a number and copy the result. Options let you leave out “and” or write it in cheque style.
How number bases work
Decimal uses ten digits. Binary uses only 0 and 1, which is how computers store everything. Hexadecimal uses 0 to 9 and A to F, so each hex digit stands for exactly four binary digits; that is why colours and memory addresses are written in hex. Prefixes such as 0x, 0b and 0o are understood. The Base row converts to another base of your choice, and Group digits adds spaces to binary and hex and commas to decimal so long numbers are easier to read.
Roman numerals
I is 1, V is 5, X is 10, L is 50, C is 100, D is 500 and M is 1000. A smaller numeral before a larger one is subtracted, as in IV for 4 and CM for 900. Standard Roman numerals go up to 3999 (MMMCMXCIX).
Writing numbers in words
British English puts “and” after hundreds, as in one hundred and five; American English often leaves it out. The check style writes dollars in words and cents as a fraction, such as One thousand two hundred fifty and 50/100. It is handy for cheques, contracts and lesson plans.
Handy examples
- Decimal 255 is binary 11111111 and hexadecimal FF.
- Decimal 2026 is MMXXVI in Roman numerals.
- Hex 1A is decimal 26.
Who uses it
Students learning computer science, programmers reading memory values or colour codes, teachers preparing worksheets, and anyone writing a date in Roman numerals for a film credit, a clock face or a tattoo. For colour codes, the colour converter goes further, and the text to binary tool converts words.
Questions
Why is there no Roman numeral for zero or above 3999?
Standard Roman numerals have no zero, and they stop at 3999 because there is no standard symbol for 5000.
How do I convert binary to decimal?
Type the binary number in the Binary row and read the Decimal row.
Is anything sent to a server?
No. Everything is worked out in your browser.